A DVD player plays back information stored on a DVD. DVD, an acronym for Digital Video Disc or Digital Versatile Disc, is a relatively new type of Compact-Disc Read-Only-Memory (CD-ROM). With a minimum capacity of approximately 4.7 gigabytes, a DVD can store a full length movie. A DVD player includes an Optical Pick-up Unit (OPU), a Read channel, and a digital video decoder. The OPU converts information read from the DVD into an analog RF signal. The Read Channel takes this RF signal and generates a digital data signal and a synchronous clock signal. The Read Channel couples these signals to a digital video decoder, which decodes the data and converts it into a video format compatible with a TV.
Previously, DVD Read Channels were implemented with analog technology. Analog implementation allows a Read Channel to remove the large DC component that typically forms part of the RF input signal from the OPU with relative ease and minor effect upon the data and clock signals. Unchecked, the low frequency disturbance of the RF input signal can cause the amplitude of the output signal to exceed the expected peak-to-peak amplitude, which can negatively impact the performance of the digital video decoder. Additionally, the baseline wandering resulting from low frequency disturbances of the RF input signal can cause so much clock jitter that the Read Channel phase lock loop (PLL) used to generate the clock may lose lock.
Various considerations now push toward a digital implementation of DVD Read Channels and, in particular, toward Partial Response Maximum Likelihood (PRML) Read Channels. Digital implementation requires a new approach to removing the low frequency disturbances of the RF input signal to the RF channel so that clock jitter does not cause the PLL to lose lock and so that the amplitude of the data signal conforms to a target spectrum.